There are many current solutions to indicate the expiration of the shelf life of a product. Most require humans to locate and read the date, know the current date, and decide if the shelf life has past. There are few solutions that can measure the amount of time a product is above a set point (usually around 40 F). These also require human interpretation and decision making By creating a mechanism that invalidates the barcode, the automation provided by checkout scanners are brought into the process. This removes the source of human error. This protects the consumer from potentially harmful products. The seller is also protected from law suits resulting from being the source of a product that caused harm. Since some products are packaged in the store, integrating this into a label which can be printed using a thermal printer allows protection of a larger range of products.
Shelf life (or in some cases, used by dates) are typically a printed date based on when the product was packaged. A few, such as Timestrip (U.S. Pat. No. 7,232,253), simplify the process by having an “Expired” or similar indication. The temperature monitoring versions of these exist (some also from Timestrip). But as mentioned before a human must locate and interpret these indications.